Who would have dreamed that a screenplay originally written for Oliver Stone would somehow morph into an irresistible musical about a bargain-basement lounge act taking on a bunch of terrorists occupying a cruise ship? "The Big Time" both pastiches and adheres to the time-honored conventions of the classic Broadway musical.

Who would have dreamed that a screenplay originally written for Oliver Stone would somehow morph into a daffy but irresistible musical about a bargain-basement lounge act taking on a bunch of hostile terrorists occupying a cruise ship? Recalling “Silk Stockings” in its wry view of Eastern Bloc subversives being seduced over to decadent Western ways by the dazzle of showbiz, “The Big Time” both pastiches and adheres to the time-honored conventions of the classic Broadway musical. Presented as part of the New York Musical Theater Festival, this smartly cast show is funny stuff, offering a disarming antidote to terrorism anxiety. An Off Broadway commercial run beckons.

Playwright-screenwriter Douglas Carter Beane (“As Bees in Honey Drown”) conceived the project as a satire of Steven Seagal thriller “Under Siege,” in which a Navy SEAL-turned-cook saves the day when hijackers take over a warship, intent on stealing its nuclear arsenal. Beane’s droll riff on that material unfolds on a cruise liner commandeered for a U.N. Peace Conference in neutral territory. The intruders are a band of Uzi-toting terrorists from the Dreggish Republic, a breakaway nation from Pedestria (“We are not Pedestrians! We are the Dregs!”).

In a book that stacks up the mistaken-identity scenarios with infectious abandon, D-list club crooners Tony and Donna Stevenitti (Sal Viviano, Debbie Gravitte) are booked on the cruise by British diplomat Penelope (Joanna Glushak), under the impression they are Steve and Eydie (as in Lawrence and Gorme). Tony and Donna, in turn, are convinced they’re playing a gay cruise, which Donna swears will be her last attempt to make their failed act and failing relationship work. But the ship’s lavish buffet and an encounter with CIA agent Big Apple (Bradley Dean), who she believes is from CAA, persuade Donna that Tony might have steered them onto a lucky streak.

When the waiters whip out their weapons during the Stevenittis’ opening set (“Tough crowd,” deadpans Donna), the singers, diplomats and agents are bundled off into confinement. As the terrorists prepare to assert their power by holding the entire U.N. peace council hostage, Donna galvanizes the dispirited band into action, identifying the hijackers Achilles’ heel as their secret passion for Western showbiz.

One of the high points among the consistently witty songs by Douglas J. Cohen is “Western Ways,” in which the clueless terrorists, led by brooding Residu (Michael McCormick), denounce the sickness of everything from Fosse to big bands, “Mikhail” Bennett to June Taylor: “Never knew what pain meant/Before Western entertainment.”

Beane and Cohen’s thorough grounding in showbiz lore and in the structural mechanics of the Broadway musical make “The Big Time” play like a parody on the order of “The Musical of Musicals: The Musical!” but one in which the spoofing is a secondary engine to the fully developed narrative and characters.

While director Christopher Ashley’s jaunty handle on the material doesn’t entirely disguise some flat patches and shaky plotting as the hostages move to regain power, the show’s boisterous spirit and warmly beating heart will not be denied.

The low-rent charms of Robert Bissinger’s shipboard set (with a tacky tinsel curtain stretched across for the Atlantic City casino opening) sits just fine with tongue-in-cheek material that undoubtedly would look plain cheesy in a slick Broadway inflation.

Cohen’s songs perhaps could stand more robust backing, but even with the two-piece accompaniment here, tunes are catchy and full-bodied.

As the trashy South Philly duo singing for world peace, Gravitte and Viviano are perfect. Burned out on playing lousy gigs and waiting around for Tony to marry her for real, Donna’s wistful, romantic side is revealed in “I Could Get Used to That,” while Gravitte’s stage-vet brassiness surfaces to delightful effect as she remains cool and savvy even during the most life-threatening situations: “Honey, I’ve sung Sondheim.” Bouffant-haired Viviano also hits the right notes as the gum-popping, finger-snapping lug who comes through in a crunch. Tony’s “A Guy Without a Girl” is prime Rat Pack-meets-Cole Porter.

Buoyed by Daniel Pelzig’s amusing, old-school choreography, the numbers allow each appealing cast member a turn in the spotlight. Among the most enjoyable is the British Ambassador (Patrick Quinn) dissing the leaden logic of international diplomacy in favor of musical fantasy in “Big, Brash, Splashy and Illogical Musical”; the rousing act one closer, “We Are Gonna Save the World,” in which the hostages and terrorists fervently outline their missions; and the jazzy title song.

Rather than leaning heavily on the post-9/11 relevance, Beane and Cohen refuse to demonize even the most fanatical of the terrorists. Instead, the motley band is sketched as misguided, lonely souls, imprisoned by their longing for Burns & Allen comedy routines, Broadway chorus lines and Glenn Miller orchestrations. (As big-band fan Grusha, rubber-faced Jackie Hoffman steals the show whenever she’s onstage.)

Blithely proposing showbiz glitz as a cure-all for war, terrorism and even starchy diplomacy, this effusive musical offers sweet, silly escape.

The Big Time

Lion Theater; 88 seats; $25 top

• Production:A New York Musical Theater Festival, Drama Dept. presentation of a musical in two acts, with music and lyrics by Douglas J. Cohen, book by Douglas Carter Beane. Directed by Christopher Ashley. Musical director, Jonathan Smith. Choreography, Daniel Pelzig.
• Crew:Sets, Robert Bissinger; costumes, David Zinn; lighting, Jeff Croiter; production stage manager, Adam Grosswirth. Opened Sept. 16, 2005. Reviewed Sept. 20. Running time: 2 HOURS.
• Cast:Announcer, Mimke, Chief - Raymond Bokhour Donna Stevenitti - Debbie Gravitte Tony Stevenitti - Sal Viviano Drunk, Ambassador Briggs-Hopkins - Patrick Quinn Morty, Residu - Michael McCormick Naomi, Grusha - Jackie Hoffman Penelope - Joanna Glushak Big Apple - Bradley Dean Pavlov - David Beach